1. Field of the Invention
The present invention relates to a radiation imaging system and a relay station selection method.
2. Description of the Related Art
There is known a radiation imaging system which captures a radiographic image of an object by irradiating an object with radiation (for example, X-rays) and detecting the intensity distribution of the radiation transmitted through the object. Such a system is widely used in the medical and industrial fields and the like.
Such radiography sometimes uses a semiconductor sensor like that disclosed in Japanese Patent Laid-Open No. 8-116044. Radiography using a semiconductor sensor can obtain a very wide dynamic range as compared with conventional radiography using photosensitive films, and hence can obtain radiographic images which are free from the influences of variations in the radiation dose upon exposure. In addition, unlike the conventional photosensitive film scheme, this technique need not perform any chemical process and can instantly obtain an output image. An imaging system using a semiconductor sensor is mainly divided into a radiation imaging unit to acquire images and a control unit to control the image acquisition of the imaging unit and display captured images on a monitor.
Recently, a flat, lightweight, portable imaging unit (also called an electronic cassette) has been required to allow quicker radiography of regions in a wider range. A high-speed communication cable has been used between the imaging unit and the control unit to implement real-time image display. Such a cable, however, becomes an obstacle when the operator moves the portable imaging unit or installs the imaging unit in a desired position. This degrades the operability. For the sake of an improvement in communication performance by wireless as well, a wireless electronic cassette like that disclosed in Japanese Patent Laid-Open No. 2003-210444 has also been proposed.
There are various types of detector holders to position an electronic cassette to a subject in accordance with a desired imaging form. Such detector holders include a stand for chest radiography to be performed in a standing position and an imaging table in a decubitus state. Each detector holder includes a housing unit to mount an electronic cassette. The housing unit holds the electronic cassette so as to properly position it with respect to a radiation generator.
In general, a housing unit is often formed from a metal housing which contains an electronic cassette. The metal housing becomes a factor that degrades wireless communication performance between a wireless antenna built in the electronic cassette and an external wireless communication unit connected to the control unit.
In addition, such an external wireless communication unit is generally provided singly. That is, such a system has not been configured to perform wireless communication between the electronic cassette and the control unit upon selecting one of a plurality of wireless communication units.